Imidazolium salts hydroxy

Chung et al. reported the enantioselective synthesis of chiral NHCs, such as 6, using a chiral ferrocene derivative (Scheme 8) [28]. The nucleophilic substitution of the hydroxy function by an imidazole in an acidic medium gives the imidazolium salt with retention of the configuration at the chiral C-atom. 

Figure 3.59 Synthesis and derivatisation of a hydroxy functionalised imidazolium salt.

Schwarz et al. [326] synthesised a functionalised bis-imidazolium salt with hydroxy end groups on the wingtips [327,328] and used it in the formation of chelating cw-bis-carbene complexes of palladium(ll) applied as catalysts in the Heck reaction. The functional groups were needed to immobilise the catalyst by attachment to a polymeric support [329] (see Figure 3.104). 

Figure 4.3 Synthesis of a hydroxy cyclohexyl functionalised imidazolium salt and its copperf II) complexes.

The epoxide can provide another reactive functional group in order to engage two imidazole molecules in simultaneous quartemisation reactions thus producing a hydroxy functionalised bis-imidazolium salt that can be used as a tridentate ligand. Such an example was reported by Arnold et al. in the reaction between 2 equiv. of A-tert-butyl imidazole and... 

Figure 4.4 Syntheses of a hydroxy functionalised bis-imidazolium salt and its silver(l) and copper I) complexes.

Once the hydroxy functionalised imidazolium salt is formed, it can be deprotonised and reacted with various metal complexes to form (transition) metal carbene complexes. The hydroxy group ensures that the ligand can be coordinated even to metals that are normally reluctant to form stable carbene complexes. A good example is the deprotonation of a hydroxyethyl functionalised imidazolium salt with potassium hydride [36]. The potassium cation coordinates to the oxygen atom of the alkoxide sidechain and forms cubes as structural elements (see Figure 4.6). The carbene end then coordinates to the respective... 

When the alkyl halide method is used to introduce a hydroxy functional group it can as easily provide two hydroxy functionahties in the same wingtip group. An example comes from Cai et al. who reacted A-methylimidazole with 3-chloro-2-hydroxypropanol to form the corresponding imidazolium salt (see Figure 4.13) that was then used in the palladium catalysed Heck reaction between phenyl iodide and ethyl acrylate [51]. 

Milione et al. reacted the same phenoxyimino functionalised imidazolium salt with trialkyl alanes in an attempt to form the corresponding carbene complex of aluminium(III) [71] (see Figure 4.19). Reaction of the phenoxyimino functionalised imidazolium salt with AIMOj proceeds smoothly with the hydroxy group reacting with the alane under elimination of methane. The imidazolium end does not react under methane elimination, but remains pendant. Aluminium carbene adducts are still rare [72-75] and are usually synthesised by a reaction between the alane and the free carbene. 

The simpler architecture is the 1,1 -biphenyl scaffold, likewise introduced by Hoveyda and coworkers [19]. The synthesis of the imidazolium salt starts with a chiral diamine and a substituted, achiral biphenyl [82-84], Subsequent introduction of a Mes substituent on the remaining primary amino end and ring closure reaction yields the chiral saturated imidazolium salt after hydrolysation of the methoxy group to liberate the phenolic hydroxy group (see Figure 4.22). Reaction with silver(I) oxide and carbene transfer to a Grubbs (Hoveyda) catalyst sets up the ruthenium catalyst complex. 

The protocol leading to the unsaturated 1,1 -hydroxy-binaphthyl saturated NHC was a chance discovery, enabled by an aqueous workup procedure. The yield is only moderate (40%) and has to be separated from the main product, the targeted bis-imidazolium salt (51%). A better synthesis for this ligand might be desirable, although the saturated NHC equivalent is readily available [18,86,88,89]. 

The hydroxy-binaphthyl functionalised saturated imidazolium salt is readily available from 1-amino-I -hydroxy-binaphthyl in a reaction with a ( oc-protected mesitylamine aldehyde [86] (see Figure 4.24). The resulting Schiff base is reduced to the diamine by Na(OAc)3BH. Subsequent deprotection and ring closure reaction with triethyl orthoformate yields the corresponding hydroxy-binaphthyl functionalised saturated imidazolium salt. Reaction with silver(I) carbonate and subsequent carbene transfer to the ruthenium(II) precursor yields the asymmetric olefin metathesis precatalyst. 

Figure 4.24 Synthesis of a hydroxy-binaphthyl functionalised imidazolium salt.

Figure 5.20 Synthesis of a chiral hydroxy functionalised imidazolium salt on an axially chiral 1,1 -binaphthyl scaffold.

Both nitronium and nitrosonium salts are effective initiators but with quite different results. Thus, propene and nitronium fluoroborate react to produce the secondary a-nitrocarbenium ion which undergoes Ritter reaction with acetonitrile to yield amide (118). Under similar conditions, nitrosonium fluoroborate leads to heterocyclic products. Intramolecular reaction of the nitroso and nitrilium groups, followed by prototropic shifts, affords the iV-hydroxy imidazolium salt (119). This may be either neutralized to produce the iV-oxide or reduced to the imidazole (120 Scheme SS). 

Glyoxal reacts with primary amines to give diazadienes which cyclize in the presence of dry HCl to form imidazolium salts <86CB1868>. Similar methods have b n applied to the synthesis of imidazoline and benzimidazole 1-oxides (or their tautomers). Thus, 1-hydroxylamino oximes react at room temperature with formaldehyde (or on heating with other aldehydes) to give 1-hydroxy-3-... 

Several other methodologies have been employed for the synthesis of hydroxy-lated TSILs. 2-Hydroxypropyl-fiinctionalized imidazolium salts have been prepared in excellent yields by the reaction of protonated 1-methylimidazole with propylene oxide, the acid providing the anionic component of the resultant ionic liquid (Scheme 5.5-4) [22]. 

C5H9N2O3PS, 2-Hydroxy-1,3,2-dioxaphospholane 2-sulfide imidazolium salt, 44B, 600... 

The SEE diagram for a longer alkyl chain IL (2-hydroxy-ethyl)dimethyl undecyloxymethylammonium dicyanamide, [CnOCiEtOH(Ci)2N][dca] (1) in 1-octanol presents a typical SLE/LLE phase diagram—a simple eutectic system with immiscibility in the liquid phase with the UCST. The influence of the [dca] anion in spite of the long alkyl chain makes this salt liquid at room temperature = 283.5 K). Therefore, the choice of the anion can have a huge effect on the phase behavior of ammonium and imidazolium ILs. 

Dihydro-1-(2-hydroxyethyl)-3-(2-hydroxy-3-sulfonatopropyl)-2-undecyl-1H-imidazolium, monosodium salt. See Sodium lauroamphohydroxypropylsulfonate... 

Sodium lauroamphohydroxypropylsulfonate CAS 68039-23-6 EINECS/ELINCS 268-242-1 Synonyms 4,5-Dihydro-1 -(2-hydroxyethyl)-3-(2-hydroxy-3-sulfonatopropyl)-2-undecyl-1H-imidazolium, monosodium salt IH-lmidazolium, 4,5-dihydro1-(2-hydroxyethyl)-3-(2-hydroxy-3-sulfopropyl)-2-undecyl-, hydroxide, inner salt, monosodium salt Lauroamphohydroxypropylsulfonate Lauroamphopropylsulfonate ... 

Laus and his colleagues are responsible for a valuable and extensive series of studies of imidazolium derivatives that includes the crystallographic characterisation of a series of N-hydroxy, alkoxy and amino salts. Among these, a pairwise conparison may be made between [(RO)2im][PF0] [93] data collected at 233 K] R = Me (syn form) (mpt. 83-84°C U l 466 kJ... 

Eight ionic liquid iV-amino and iV-hydroxy salts of imidazole have been prepared and characterised, permitting the following comparisons in which hydrogen-bond donor and acceptor groups are linked directly to the imidazolium ring nitrogens [(H2N)2(2-Me)im]... 

Imidazolium compds., 1-[2-(carboxymethoxy) ethyl]-4,5-dihydro-1-(2-hydroxy-ethyl)-2-nortallow all l, hydroxides, inner salts. See Sodium tal-lowamphoacetate... 

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